Gilbert H. Denny was born around 1842 in Indiana to Morris Denny. His father was a farmer who owned $1,000 of real estate and $450 of personal property by 1860. He grew up and attended school in Washington County, Indiana, and by 1860, he was working as a farm laborer. He enlisted in the Union army on August 16, 1861, and he mustered in as a private in Company G of the 18th Indiana Infantry later that day. He was eventually promoted to sergeant. The regiment took part in the Battle of Pea Ridge and the Siege of Vicksburg, and he died in Baltimore, Maryland, on March 19, 1865.